Well, once you're in that situation, you've already lost. Scrum is worthless if you haven't set he appropriate expectations with stakeholders at the outset. If you get them to understand definitions of Ready and Done as well as quality-first approach and being flexible on scope, then the backlog gives them all the information they need to understand what is being worked on and when. I've seen it done correctly a few times and I've even seen behemoth organizations get behind it and get a ton of value out of it.

For my money, the #1 benefit to scrum is improved visibility to stakeholders and any productivity gains to the dev are the result of them being able to work on things in the correct priority order due mainly to benefit #1.